Annual report pursuant to Section 13 and 15(d)

Supplemental Information On Oil And Gas Exploration And Production Activities (Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details)

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Supplemental Information On Oil And Gas Exploration And Production Activities (Standardized Measure Of Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves) (Details) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Supplemental Information On Oil And Gas Exploration And Production Activities [Abstract]      
Future cash flows $ 1,594,050,000 $ 1,479,295,000 $ 1,005,029,000
Future development and abandonment costs (306,810,000) (301,651,000) (209,975,000)
Future production costs (295,383,000) (305,814,000) (236,003,000)
Future production taxes (124,739,000) (136,323,000) (97,841,000)
Future income taxes (229,649,000) (159,171,000) (50,229,000)
Future net cash flows 637,469,000 576,336,000 410,981,000
10% discount to reflect timing of cash flows (260,788,000) (260,849,000) (170,207,000)
Standardized measure of discounted future net cash flows $ 376,681,000 $ 315,487,000 $ 240,774,000